Power systems with current regulation

ABSTRACT

A power system includes a current regulator coupled to a load and for generating an output current having a substantially constant ripple magnitude, and for adjusting the output current according to a sense signal indicative of the output current. In addition, the power system includes a filter element coupled in parallel with the load and for passing an AC (alternating-current) portion of the output current. Furthermore, the power system includes a current sensor coupled between ground and the parallel-coupled filtering element and load, and for providing the sense signal indicative of the output current.

TECHNICAL FIELD

Embodiments in accordance with the present invention relate to powersystems with current regulation.

BACKGROUND ART

Currently, light sources such as LEDs (light emitting diodes) can beused in many applications, such as traffic lights, backlight for LCD(liquid crystal display) TVs, computer monitors, etc. In conventionalLED driven systems, linear regulators can be used to drive the LEDs.However, a considerate amount of power may be dissipated on the linearregulators, which may reduce the efficiency of the regulators. Inaddition, the conventional regulators may not regulate an output currentto a desirable level accurately enough.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthis specification, illustrate embodiment of the present invention and,together with the description, serve to explain the principles of theinvention:

FIG. 1 illustrates an exemplary block diagram of a power system, inaccordance with one embodiment of the present invention.

FIG. 2 illustrates an exemplary plot for an output current generated bythe power system, in accordance with one embodiment of the presentinvention.

FIG. 3 illustrates an exemplary block diagram of a display system, inaccordance with one embodiment of the present invention.

FIG. 4 illustrates an exemplary flowchart of operations performed by apower system, in accordance with one embodiment of the presentinvention.

SUMMARY

In one embodiment, a power system includes a current regulator coupledto a load and for generating an output current having a substantiallyconstant ripple magnitude, and for adjusting the output currentaccording to a sense signal indicative of the output current. Inaddition, the power system includes a filter element coupled in parallelwith the load and for passing an AC (alternating-current) portion of theoutput current. Furthermore, the power system includes a current sensorcoupled between ground and the parallel-coupled filtering element andload, and for providing the sense signal indicative of the outputcurrent.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of the presentinvention. While the invention will be described in conjunction withthese embodiments, it will be understood that they are not intended tolimit the invention to these embodiments. On the contrary, the inventionis intended to cover alternatives, modifications and equivalents, whichmay be included within the spirit and scope of the invention as definedby the appended claims.

Furthermore, in the following detailed description of the presentinvention, numerous specific details are set forth in order to provide athorough understanding of the present invention. However, it will berecognized by one of ordinary skill in the art that the presentinvention may be practiced without these specific details. In otherinstances, well known methods, procedures, components, and circuits havenot been described in detail as not to unnecessarily obscure aspects ofthe present invention.

In one embodiment, the present invention provides a power system forpowering a load. Since the power system in the present invention employsa switching regulator, the power consumption can be reduced. In one suchembodiment, the power system can generate an output current having asubstantially constant ripple current, and adjust a DC (direct current)level of the output current to a proper level to power the load. Theoutput current can be controlled/adjusted by comparing a sense signalwith a reference signal by a controller. In one embodiment, the sensesignal indicating both AC (alternating current) level and DC level ofthe output current is feedback to the controller for output currentcontrol. As such, the output current (e.g., the DC level and/or the AClevel of the output current) can be controlled in a relatively accurateway. In addition, the sense signal can be a voltage signal with respectto ground, and the voltage level of the sense signal can be relativelylow, which can further decrease power consumption of the power system.

In one embodiment, the present invention also provides an exemplarydisplay system. In one such embodiment, the aforementioned power systemcan be used to power a set of light sources (e., a red-light emittingdiode, a green-light emitting diode and a blue-light emitting diode) inthe display system. In addition, an intensity controller can be used tocontrol an intensity of light emitted from each light source, so as tocontrol a hue of the color mixed by the lights emitted from the set oflight sources.

FIG. 1 illustrates an exemplary block diagram of a power system 100, inaccordance with one embodiment of the present invention. In oneembodiment, the power system 100 includes a current regulator 102 (e.g.,a switching regulator) coupled to a load 104. The current regulator 102can receive an input voltage V_(IN) and generate an output current 10having a substantially constant ripple magnitude, and adjust the outputcurrent lo according to a sense signal (e.g., a voltage signal V_(CS)shown in FIG. 1) indicative of the output current I₀. More specifically,the current regulator 102 can adjust the output current I₀ by comparinga predetermined reference signal (e.g., a reference voltage V_(PRE)shown in FIG. 1) with the sense signal V_(CS). The power system 100 canalso include a filter element 106 (e.g., a capacitor) coupled inparallel with the load 104 and for passing an AC portion I_(AC) of theoutput current I₀, and for blocking a DC portion I_(DC) of the outputcurrent I₀. In addition, the power system 100 can include a currentsensor 108 coupled between ground and the parallel-coupled filteringelement 106 and load 104, and for providing the sense signal V_(CS).

More specifically, the current regulator 102 can include a comparator118 for comparing the sense signal V_(CS) with the predeterminedreference signal V_(PRE) and for generating a control signal 122according to a result of the comparison. The current regulator 102 canfurther includes a controller 120 (e.g., a constant ripple currentcontroller) coupled to the comparator 118 and for generating a PWM(pulse width modulation) signal 1 12 based on the control signal 122 tocontrol the output current I₀. For example, the constant ripple currentcontroller 120 can generate a PWM signal having a first state (e.g.,high) for a time period T_(ON) and having a second state (e.g., low) fora time period T_(OFF). T_(ON) can be inversely proportional to adifference between a signal S_(IN) representative of the input voltageV_(IN) of the current regulator 102 and a signal S_(OUT) representativeof an output voltage V_(OUT) of the current regulator 102. T_(OFF) canbe inversely proportional to S_(OUT). In another embodiment, thecomparator 118 can be included in the controller 120.

In one embodiment, the PWM signal 112 controls a high-side switch 114coupled between the input voltage source V_(IN) and an inductor 110, andcontrols a low-side switch 116 coupled between the inductor 110 andground.

In the example of FIG. 1, the comparator 118 coupled to the resistor 108is operable for receiving the sense signal V_(CS) and the predeterminedreference signal V_(PRE). In one embodiment, the current sensor 108 canbe a resistor for passing the current I₀ and for generating the sensesignal V_(CS) indicative of the output current I₀ (e.g., V_(CS) is equalto the current I₀ multiplied by a resistance R_(CS) of the resistor 108,V_(CS)=I₀*R_(CS)). The comparator 118 can generate a control signal 122according to a comparison result of the sense signal V_(CS) and thepredetermined reference signal V_(PRE).

As described above, the controller 120 can be a CRC (constant ripplecurrent) controller. For example, when the signal V_(CS) decreases tothe signal V_(PRE), the control signal 122 can control the controller120 to generate a high PWM signal 112 to turn on switch 114 and turn offswitch 116 so as to increase the current I₀. In addition, a time periodT_(ON) when the PWM signal 112 is high can be controlled by thecontroller 120, and the controller 120 can generate a low PWM signal 112after the time period T_(ON) expires. During the time period T_(OFF)when the PWM signal 112 is low, switch 114 is turned off and switch 116is turned on, such that the current I₀ starts to decrease, and so doesthe sense signal V_(CS). Thus, the controller 120 can adjust the dutycycle of the PWM signal 112 (e.g., by controlling the time periodT_(ON)) such that the current I₀ can be no less than the current valueV_(PRE)/R_(CS) and have a ripple magnitude ΔI₀. In one embodiment, thecontroller 120 can control the duty cycle of the PWM signal 112 so as tomaintain the ripple magnitude ΔI₀ substantially constant. The ripplemagnitude ΔI₀ can vary but within a range such that an equivalentcurrent level I_(EQV) of the current I₀ can be relatively stable.

An exemplary plot 200 for the output current I₀ is illustrated in FIG.2, in accordance with one embodiment of the present invention. FIG. 2 isdescribed in combination with FIG. 1. As shown in the example of FIG. 2,a high state of the PWM signal 112 can be triggered when the outputcurrent I₀ decreases to the current level V_(PRE)/R_(CS). The ripplemagnitude ΔI₀ can be substantially constant. Additionally, the waveformof the output current I₀ can be a sawtooth waveform as depicted in FIG.2. As such, the equivalent current level I_(EQV) of the current 1o canbe given by:

I _(EQV) =V _(PRE) /R _(CS) +ΔI ₀/2.   (1)

The load 104 in FIG. 1 can include one or more LEDs (light emittingdiodes), e.g., an LED string. The filter element 106 in FIG. 1 can be acapacitor. The current I₀ can include an AC I_(AC) flowing through thecapacitor 106 and a substantial DC I_(DC) flowing through the LEDs 104.If the waveform of the current I₀ is a sawtooth, the AC portion I_(AC)of I₀ can also have a sawtooth waveform as depicted in FIG. 2. Inaddition, in one embodiment, the level of the current I_(DC) flowingthrough the LEDs 104 can be equal to the equivalent current levelI_(EQV) of the current I₀, for example:

I _(DC) =I _(EQV) =V _(PRE) /R _(CS) +ΔI ₀/2.   (2)

Since the ripple magnitude ΔI₀ can be substantially constant, thecurrent I_(DC) can be relatively stable to drive the LEDs 104 with adesirable light intensity. In one embodiment, the current level I_(DC)of the DC portion can be determined by the predetermined referencesignal V_(PRE).

Advantageously, since the current I₀ can be regulated by comparing thereference signal V_(PRE) with the sense signal V_(CS) indicative of theboth DC and AC levels of the current I₀, regulation of the current I₀(e.g., regulation of the level of I_(DC) and/or the level of I_(AC)) canbe relatively accurate. Furthermore, since the resistor 108 in FIG. 1 iscoupled between ground and the parallel-coupled capacitor 106 and LEDs104 and can have a relatively low resistance R_(CS), the sense signalV_(CS) and the reference signal V_(PRE) can have relatively low voltagelevels. As such, the power consumption can be decreased and the systemefficiency can be increased, in one embodiment.

FIG. 3 illustrates an exemplary block diagram of a display system 300,in accordance with one embodiment of the present invention. Elementslabeled the same as in FIG. 1 have similar functions and will not berepetitively described herein. As shown in FIG. 3, the display system300 includes a plurality of light sources 304 for emitting a mixedcolor. In addition, the display system 300 also includes a currentregulator 102 for generating a current lo having a substantiallyconstant ripple magnitude and for adjusting the current 10 based on anadjust signal 324.

Furthermore, the display system 300 includes an intensity controller 330coupled to the current regulator 102 and for receiving a plurality ofintensity control signals 336 and a plurality of select signals 338. Theintensity controller 330 can generate the adjust signal 324 based on theintensity control signals 336 and the select signals 338, and control ahue of the mixed color according to the adjust signal 324.

In the example of FIG. 3, the plurality of light sources 304 includes afirst LED 304_1 for emitting a red color, a second LED 304_2 foremitting a green color and a third 304_3 LED for emitting a blue color.Correspondingly, the plurality of intensity control signals 336 caninclude an intensity control signal 336_1 for controlling the currentflowing through the first LED 304_1, an intensity control signal 336_2for controlling the current flowing through the second LED 304_2, and anintensity control signal 336_3 for controlling the current flowingthrough the third LED 304_3. Each intensity control signal 336-1_336-3can indicate a predetermined/desirable light intensity of acorresponding LED 304-1_3-4_3. The light sources 304 can include anynumber of LEDs. In an alternate embodiment, the light sources 304 caninclude other types of light sources.

In addition, in one such embodiment, a plurality of switches 328_1-328_3can be respectively coupled to the light sources 304_1-304_3 forallowing a DC portion I_(DC) of the current I₀ to flow through acorresponding light source 304_1-304_3 based on the select signals338_1-338_3. For example, as shown in FIG. 3, the select signal 338_1can switch on the corresponding switch 328_1 coupled to the light source304_1, and at the meantime the select signals 338_2-338_3 can switch offthe switches 328_2-328_3, so as to allow the DC I_(DC) to flow throughthe light source 304_1. Light source 304_2 or 304_3 can be controlled ina similar manner.

Furthermore, the select signal 338_1-338_3 can select a correspondingcontrol signal 336_1-336_3 to control the DC I_(DC) flowing through acorresponding light source 304_1-304_3. More specifically, the intensitycontroller 330 can include a multiplexer 334 for receiving the intensitycontrol signals 336_1-336_3 and the select signals 338_1-338_3, and foroutputting a selected intensity control signal of the intensity controlsignals 336_1-336_3 based on the select signals 338_1-338_3. Each selectsignal 338_1-338_3 can be a pulse signal. In addition, the selectsignals 338_1-338_3 can be phases-shifted. For example, when one selectsignal is high and the other select signals are low, the multiplexer 334can output a corresponding selected intensity control signal336_1-336_3, and a corresponding switch 328_1-328_3 can be turned on. Assuch, the selected intensity control signal 336_1-336_3 can control theDC I_(DC) flowing through the corresponding light source 304_1-304_3 fora time interval ΔT′ during which the corresponding intensity controlsignal is selected.

In the example of FIG. 3, the intensity control signal 336_1-336_3 canbe a digital signal, and the adjust signal 324 can be an analog signal.A D/A (digital-to-analog) converter 332 can be coupled to themultiplexer 334 and convert the selected intensity control signal to theadjust signal. In one embodiment, the adjust signal 324 at the outputterminal of the D/A converter 332 can have a voltage level V_(DAC). Asshown in FIG. 3, the output terminal of the D/A converter 332 can becoupled to the current regulator 102 at a connection node 326 via aresistor 342. The connection node 326 can be further coupled to thecurrent sensor resistor 108 via a resistor 344. The current senseresistor 108 can provide the sense signal V_(CS). As such, in oneembodiment, a feedback signal (e.g., a voltage signal V_(F) shown inFIG. 3) at the connection node 326 can be determined by the adjustsignal 324 indicative of a predetermined light intensity of acorresponding LED 304-1_304_3 and the sense signal V_(CS) indicative ofthe output current I₀. The comparator 118 can compare the feedbacksignal V_(F) with the reference signal V_(PRE) so as to control thecontroller 120 to adjust the output current I₀.

In one embodiment, according to the superposition theory, the feedbacksignal V_(F) can be given by:

V _(F) =V′ _(F) +V″ _(F),   (3)

where V′_(F) is a voltage level at the connection node 326 when thevoltage level V_(DAC) is assumed to be zero, and V″_(F) is a voltagelevel at the connection node 326 when the voltage level V_(CS) isassumed to be zero. If the voltage level V_(DAC) is zero, the voltageV′_(F) can be given by:

$\begin{matrix}{{V_{F}^{\prime} = {V_{CS} \times \frac{R_{1}}{R_{1} + R_{2}}}},} & (4)\end{matrix}$

where R₁ is the resistance of the resistor 342, and R₂ is the resistanceof the resistor 344. If the voltage level V_(CS) is zero, the voltageV″_(F) can be given by:

$\begin{matrix}{V_{F}^{''} = {V_{DAC} \times {\frac{R_{2}}{R_{1} + R_{2}}.}}} & (5)\end{matrix}$

As such, the feedback signal V_(F) can be given by:

$\begin{matrix}{V_{F} = {{V_{F}^{\prime} + V_{F}^{''}} = {\frac{{V_{CS} \times R_{1}} + {V_{DAC} \times R_{2}}}{R_{1} + R_{2}}.}}} & (6)\end{matrix}$

In one embodiment, when the feedback voltage V_(F) is equal to thereference voltage V_(PRE), the following equation can be obtained:

$\begin{matrix}{V_{PRE} = {V_{F} = {\frac{{V_{CS} \times R_{1}} + {V_{DAC} \times R_{2}}}{R_{1} + R_{2}}.}}} & (7)\end{matrix}$

The equation (7) can be rewritten as:

$\begin{matrix}{V_{CS} = {\frac{{V_{PRE} \times \left( {R_{1} + R_{2}} \right)} - {V_{DAC} \times R_{2}}}{R_{1}}.}} & (8)\end{matrix}$

As such, when the feedback voltage V_(F) is equal to the referencevoltage V_(PRE), a current I_(CS) flowing through the sense resistor 108can be given by:

$\begin{matrix}{I_{CS} = {{V_{CS}/R_{CS}} = {\frac{{V_{PRE} \times \left( {R_{1} + R_{2}} \right)} - {V_{DAC} \times R_{2}}}{R_{1} \times R_{CS}}.}}} & (9)\end{matrix}$

In the example of FIG. 3, the feedback signal V_(F) can be no less thanthe reference signal V_(PRE), e.g., the current I₀ can be controlled noless than the current I_(CS). In addition, the ripple magnitude ΔI₀ ofthe current I₀ can be maintained at substantially constant magnitude. Inone embodiment, the waveform of the current I₀ can be a sawtoothwaveform, such that an equivalent current level I′_(EQV) of the currentI₀ can be given by:

$\begin{matrix}{I_{EQV}^{\prime} = {{I_{CS} + {\Delta \; {I_{0}/2}}} = {\frac{{V_{PRE} \times \left( {R_{1} + R_{2}} \right)} - {V_{DAC} \times R_{2}}}{R_{1} \times R_{CS}} + {\Delta \; {I_{0}/2.}}}}} & (10)\end{matrix}$

Since the DC portion I_(DC) of the current I₀ can be substantially equalto the equivalent current I′_(EQV) of the current I₀ as described inrelation to FIG. 1 and FIG. 2, I_(DC) can be given by:

$\begin{matrix}{I_{DC} = {I_{EQV}^{\prime} = {\frac{{V_{PRE} \times \left( {R_{1} + R_{2}} \right)} - {V_{DAC} \times R_{2}}}{R_{1} \times R_{CS}} + {\Delta \; {I_{0}/2.}}}}} & (11)\end{matrix}$

As such, the current I_(DC) can decrease when the adjust signal 324increases, in one embodiment. Accordingly, an intensity of the lightemitted from a corresponding light source 304_1-304_3 through which theDC portion I_(DC) flows can be adjusted by the adjust signal 324.

Since the select signals 338_1-338_3 can be phase-shifted, the DCportion I_(DC) of the current I₀ can flow through each light source304_1-304_3 for a time interval sequentially and periodically. Inaddition, the level of the DC portion I_(DC) flowing through thecorresponding light source 304_1-304_3 can be controlled by acorresponding intensity control signal 336_1-336_3. Since the currentregulator 102 can be a constant-ripple-current regulator, the DC portionI_(DC) of the current I₀ can be regulated at a desirable current levelin a relatively accurate and efficient way. Consequently, the pluralityof light sources 304_1-304_3 can emit different colors withpredetermined/desirable intensities respectively, and the mixed colorcan have a predetermined/desirable hue determined by the intensitycontrol signals 336_1-336_3.

FIG. 4 illustrates an exemplary flowchart 400 of operations performed bya power system, in accordance with one embodiment of the presentinvention. FIG. 4 is described in combination with FIG. 1 and FIG. 3.

In block 402, a current generator 102 can generate a current I₀ having asubstantially constant ripple magnitude ΔI₀.

In blocks 404 and 406, a filter element 106 coupled in parallel with aload 104 can be used to pass an AC portion I_(AC) of the current I₀, andto block a DC portion I_(DC) of the current I₀. The filter element 106can be, but is not limit to, a capacitor. The DC portion I_(DC) of thecurrent I₀ can be used to power the load 104.

In block 408, a current sensor 108 coupled between ground and theparallel-coupled filter element 106 and load 104 can provide a sensesignal V_(CS) (and/or a feedback signal V_(F)) indicative of the currentI₀.

In block 410, the current generator 102 can adjust the current I₀according to the sense signal V_(CS) (or the feedback signal V_(F)),e.g., by comparing a predetermined reference signal V_(PRE) with thesense signal V_(CS) (or the feedback signal V_(F)). For example, acomparator 118 can be used for comparing the sense signal V_(CS) (or thefeedback signal V_(F)) with the predetermined reference signal V_(PRE),and for generating a control signal 122 according to a result of thecomparison. Furthermore, a controller 120 can be used for generating aPWM signal 112 based on the control signal 122. The PWM signal 112 canbe used to control a high-side switch 114 and a low-side switch 116, soas to adjust the output current I₀.

Accordingly, in one embodiment, the present invention provides a powersystem with constant ripple current regulation. A current regulator inthe power system can generate an output current having a substantiallyconstant ripple magnitude base on a current feedback (e.g., asense/feedback signal indicative of both AC and DC level of the outputcurrent), and a DC portion of the output current can be used to power aload (e.g., one or more LEDs). The power system can be implemented in adisplay system to power a set of light sources (e.g., LEDs including ared LED, a green LED and a blue LED), such that the display system candisplay a mixed color with a predetermined/desirable hue.

While the foregoing description and drawings represent embodiments ofthe present invention, it will be understood that various additions,modifications and substitutions may be made therein without departingfrom the spirit and scope of the principles of the present invention asdefined in the accompanying claims. One skilled in the art willappreciate that the invention may be used with many modifications ofform, structure, arrangement, proportions, materials, elements, andcomponents and otherwise, used in the practice of the invention, whichare particularly adapted to specific environments and operativerequirements without departing from the principles of the presentinvention. The presently disclosed embodiments are therefore to beconsidered in all respects as illustrative and not restrictive, thescope of the invention being indicated by the appended claims and theirlegal equivalents, and not limited to the foregoing description.

1. A power system comprising: a current regulator coupled to a load andfor generating an output current having a substantially constant ripplemagnitude, and for adjusting said output current according to a sensesignal indicative of said output current; a filter element coupled inparallel with said load and for passing an AC (alternating current)portion of said output current; and a current sensor coupled betweenground and said parallel-coupled filtering element and load, and forproviding said sense signal.
 2. The power system as claimed in claim 1,wherein said filter element is operable for blocking a DC (directcurrent) portion of said output current.
 3. The power system as claimedin claim 1, wherein said current regulator comprises a comparator forcomparing said sense signal with a predetermined reference signal andfor generating a control signal according to a result of saidcomparison.
 4. The power system as claimed in claim 2, wherein saidcurrent regulator further comprises a controller coupled to saidcomparator and for generating a PWM (pulse width modulation) signalbased on said control signal to control a high-side switch coupledbetween a voltage source and an inductor, and to control a low-sideswitch coupled between said inductor and ground.
 5. The power system asclaimed in claim 1, wherein said load comprises at least one LED (lightemitting diode).
 6. The power system as claimed in claim 1, wherein saidfilter element comprises a capacitor.
 7. The power system as claimed inclaim 1, wherein said current regulator adjusts said output current bycomparing said sense signal with a predetermined reference signal.
 8. Amethod for powering a load, comprising: generating an output currenthaving a substantially constant ripple magnitude; passing an AC(alternating current) portion of said output current by a filter elementcoupled in parallel with said load; providing a sense signal indicativeof said output current by a current sensor coupled between ground andsaid parallel-coupled filter element and load; and adjusting said outputcurrent according to said sense signal.
 9. The method as claimed inclaim 8, further comprising: comparing said sense signal with apredetermined reference signal; and generating a control signalaccording to a result of said comparison.
 10. The method as claimed inclaim 9, further comprising: generating a PWM (pulse width modulation)signal based on said control signal; controlling a high-side switchcoupled between a voltage source and an inductor by said PWM signal; andcontrolling a low-side switch coupled between said inductor and groundby said PWM signal.
 11. The method as claimed in claim 8, furthercomprising: blocking a DC (direct current) portion of said outputcurrent by said filter element.
 12. The method as claimed in claim 8,wherein said load comprises at least one LED (light emitting diode). 13.The method as claimed in claim 8, wherein said filter element comprisesa capacitor.
 14. The method as claimed in claim 8, wherein said currentsensor comprises a resistor.
 15. A display system comprising: aplurality of light sources for emitting a mixed color; an intensitycontroller coupled to said light sources and for generating an adjustsignal based on a plurality of intensity control signals, and forcontrolling a hue of said mixed color according to said adjust signal;and a current regulator coupled to said intensity controller and lightsources and for generating an output current having a substantiallyconstant ripple magnitude, and for adjusting said output current basedon said adjust signal.
 16. The display system as claimed in claim 15,wherein said intensity controller further receives a plurality of selectsignals and generates said adjust signal based on said intensity controlsignals and said select signals.
 17. The display system as claimed inclaim 16, wherein each of said select signals comprises a pulse signal.18. The display system as claimed in claim 16, wherein said selectsignals are phase-shifted.
 19. The display system as claimed in claim16, further comprising: a plurality of switches respectively coupled tosaid light sources for allowing a DC (direct current) portion of saidoutput current to flow through a light source of said light sourcesbased on said select signals.
 20. The display system as claimed in claim15, wherein said intensity controller comprises a multiplexer forreceiving said intensity control signals and a plurality of selectsignals, and for outputting a selected intensity control signal of saidintensity control signals based on said select signals.
 21. The displaysystem as claimed in claim 21, wherein said intensity controller furthercomprises a digital-to-analog converter coupled to said multiplexer andfor converting said selected intensity control signal to said adjustsignal.
 22. The display system as claimed in claim 15, wherein each ofsaid intensity control signals comprises a digital signal.
 23. Thedisplay system as claimed in claim 15, wherein said adjust signalcomprises an analog signal.
 24. The display system as claimed in claim15, wherein said hue is determined by said intensity control signals.25. The display system as claimed in claim 15, wherein said currentregulator comprises a comparator for comparing a feedback signal with areference signal, and wherein said feedback signal is determined by saidadjust signal and a sense signal indicative of said output current. 26.The display system as claimed in claim 25, wherein said currentregulator further comprises a controller coupled to said comparator andfor generating a PWM (pulse width modulation) based on a comparisonresult of said comparator to control said output current.
 27. Thedisplay system as claimed in claim 15, further comprising: a capacitorcoupled in parallel with said plurality of light sources and for passingan AC (alternating current) portion of said output current, and forblocking a DC (direct current) portion of said output current; and asense resistor coupled between ground and said parallel-coupledcapacitor and light sources, and for providing a sense signal indicativeof said output current.
 28. The display system as claimed in claim 15,wherein said plurality of light sources comprise a first LED (lightemitting diode) for emitting a red color, a second LED for emitting agreen color and a third LED for emitting a blue color.